Unison File Synchronizer
Unison (not the Usenet reader) is a tool for synchronizing directories between computers in a heterogenous network. I think I’ve been searching for this program since I first started looking into backing up my laptop.
I added it to my crontab. Now my home directory on my laptop will sync with the local server every night. I also installed it on my server in Regina, so my two servers will sync a particular useful directory for me every night. This way I can download something to my laptop, transfer it over to my server, and it’ll be uploaded to Regina automatically that night.